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BUG: KCSAN: data-race in generic_write_end / mpage_process_page_bufs

write to 0xffff888120916688 of 8 bytes by task 10020 on cpu 0:
 i_size_write include/linux/fs.h:878 [inline]
 generic_write_end+0x98/0x230 fs/buffer.c:2183
 ext4_da_write_end+0x26c/0x620 fs/ext4/inode.c:3068
 generic_perform_write+0x26a/0x3f0 mm/filemap.c:3798
 ext4_buffered_write_iter+0x222/0x330 fs/ext4/file.c:270
 ext4_file_write_iter+0x2e3/0x1210
 call_write_iter include/linux/fs.h:2050 [inline]
 new_sync_write fs/read_write.c:504 [inline]
 vfs_write+0x71c/0x890 fs/read_write.c:591
 ksys_write+0xe8/0x1a0 fs/read_write.c:644
 __do_sys_write fs/read_write.c:656 [inline]
 __se_sys_write fs/read_write.c:653 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:653
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888120916688 of 8 bytes by task 10029 on cpu 1:
 i_size_read include/linux/fs.h:856 [inline]
 mpage_process_page_bufs+0x34/0x530 fs/ext4/inode.c:2182
 mpage_prepare_extent_to_map+0x5b7/0xa50 fs/ext4/inode.c:2630
 ext4_writepages+0x9b8/0x1d00 fs/ext4/inode.c:2802
 do_writepages+0x1db/0x350 mm/page-writeback.c:2352
 filemap_fdatawrite_wbc+0xd6/0xf0 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 __filemap_fdatawrite mm/filemap.c:427 [inline]
 filemap_flush+0x93/0xc0 mm/filemap.c:454
 ext4_alloc_da_blocks+0x47/0x100 fs/ext4/inode.c:3112
 __ext4_ioctl fs/ext4/ioctl.c:1338 [inline]
 ext4_ioctl+0xdaa/0x2750 fs/ext4/ioctl.c:1578
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000d59000 -> 0x0000000000d5a000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 10029 Comm: syz-executor.3 Not tainted 5.18.0-rc5-syzkaller-00207-g379c72654524 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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